"People seeking the cause of autism have been looking for a smoking gun, but
it will be more like dispersed land mines," Irva Hertz-Picciotto, PhD, MPH,
tells WebMD.

Hertz-Picciotto and colleagues at the University of California, Davis MIND
Institute analyzed mothers' residences on more than 2.4 million birth
records that included nearly 10,000 autism cases in the California Department
of Developmental Services (DDS) database.

The idea was to look for areas where there might be clusters of autism. If
the increased risk of autism in these areas could not be explained by factors
known to increase autism diagnosis, the search would be on for something in the
environment of those areas that might trigger autism.

Sure enough, Hertz-Picciotto and colleagues found 10 autism clusters -- with
at least a 70% higher incidence of autism than in the surrounding area -- in
eight regions of California.

But as it turned out, there was indeed a factor that very likely explained
the clusters. Most of the clusters were in areas where women tend to have high
educational attainment. Autism cases in all of the clusters were more likely to
be reported from families with highly educated mothers, Hertz-Picciotto
says.

"I don't think people living in these areas need to be concerned about where
their homes are. Thinking about moving away from these areas would be wholly
inappropriate," she says.

The California DDS does not go out and look for kids with autism. Parents
have to go to the DDS and seek services. Better educated women are more likely
to know about these services -- and are more likely to have access to doctors
who can diagnose their child's autism.

"The implication is that parents with better awareness of autism symptoms,
with better economic means, can better test for early warning signs and find
the right kind of help for their children. And that can contribute to increased
autism prevalence," Andy Shih, PhD, vice president of scientific affairs for
the advocacy group Autism Speaks, tells WebMD. Shih was not involved in the
California study.

On the other hand, "it is entirely possible that people with higher
education have some kind of exposure that increases autism risk,"
Hertz-Picciotto says.

But that's unlikely, she suggests. There clearly is a genetic predisposition
to autism. But genes don't explain why some people get autism and others don't.
Many researchers feel there has to be some kind of environmental trigger --
perhaps something a woman encounters during pregnancy or that a child
encounters in infancy -- that triggers the disorder in susceptible
children.

"Our study tells us probably the environmental causes of autism are not
going to be found in local contamination, at least in California,"
Hertz-Picciotto says. "Whatever the environmental contributors are, they are
probably more widespread and not linked to a hazardous local factor."

The study also suggests that there are a lot more kids with autism -- in
California, at least -- who are not getting the services they need. In Denmark,
where all kids are screened for autism, parental education doesn't raise autism risk. But it is
in the U.S. and the U.K., where access to screening is not universal.

"This calls for some thinking about what we can do to increase autism
awareness in the general population and bring services to these families, so
that parents with education and means are not the only ones able to address the
health of their children in the best possible way," Shih says.

Graduate student Karla C. Van Meter is first author of the Hertz-Picciotto
study, which appears in the January issue of Autism Research.